Emergency shower and eyewash stations are often used when there is a risk that an individual may be exposed to hazardous chemicals. One who is exposed stands under the shower (or at the eyewash) for an extended period of time to flush away any such hazardous chemicals. Hypothermia or shock can occur if one is required to stand under an emergency shower for an extended period of time under cold water, especially where the surrounding environment is cold. Emergency shower and eyewash heaters have been provided to heat the water, and can comprise water tanks which are heated to supply a steady stream of warm water. However, such tanks are expensive and the duration of the shower is limited by the size of the tank. One solution to this problem has been the use of an instantaneous water heater, where the water is heated only on demand, that is, only on use of the shower or eyewash. With such designs there is also the need for better temperature control of the water reaching the shower and eyewash.
U.S. Pat. No. 5,647,531 to Kline et al discloses a control valve system for use in emergency shower and eyewash systems. The valve system mixes cold water with hot water to regulate the temperature of the water delivered to the shower and eyewash. However, such mixing valves are relatively costly. Emergency shower and eyewash stations have also been developed with on-demand heaters having controllers which monitor the output temperature of the water from the heater and attempt to hold that temperature with a predetermined range. However, such known designs do not prevent overshoot of water temperature upon reduction of a water flow rate from a high rate to a lower rate, as occurs, for example, when either the shower or the eyewash is shut off, or the shower is shut off and the eyewash is left on, etc. It would be desirable to have an emergency shower and eyewash station with heated water which avoids problems with temperature overshoot upon reduction of the flow rate of water.